A Complete Guide to Electron Beam Machining (EBM)

Electron Beam Machining is a non-conventional procedure where you can weld, cut, or anneal some perfect cuts into materials that require extreme loads of heat. These cuts are very accurate and measured by microns. 

PRINCIPLE OF ELECTRON BEAM MACHINING.

The whole process is so delicate and precise. The main motive and principle of Electron Beam Machining are to convert the kinetic energy of an electron into heat energy. At the contact surface, their heat energy is used to vaporize the material. 

The whole process is carried out under a supervised vacuum-sealed environment. If not done in such an environment, the electron collides with the air molecules, and this leads to energy loss. This is the basic principle that is followed in Electron Beam Machining.

CONSTRUCTION STRATEGY OF ELECTRON BEAM MACHINING.

1. ELECTRON GUN.

Electron Beam Machining

Electron gun is basically called as the heart of Electron Beam Machining(EBM). It helps in generating the electron. An electron gun is a simple cathode ray tube which generates electrons and helps them attain an optimum velocity and focus at the spot. 

The cathode is made up of tungsten material. The cathode filament is heated to 2500°C that helps to emit the electron by the thermionic reaction. Keep in note that the whole environment must be vacuum-sealed.

2. ANNULAR BIAS GRID. 

It is also the most important element of Electron Beam Machining(EBM). It comes and ranks just after the electron gun. It is an anode and is connected by the negative bias. 

This helps the electron generated by the cathode to not deviate and diverge from its path and reach the next element. The velocity of the electron is almost half the light’s velocity, when electron leaves this section. This fact is interesting. Isn’t it?!

3. DEFLECTION COIL AND ELECTROMAGNETIC LENS.

The main use of these electromagnetic lens is to focus the beam created by electrons at a spot. This focusing mechanism of lens helps to produce high-intensity beam and also to produce more heat. 

This also improves the machining process. The deflecting coil doesn’t allow the beam diversion and deflection. The deflection makes sure and takes care of all electrons to move in a series so that they produce a high-intensity beam.

4. MAGNETIC LENSES.

The main motive and principle of these magnetic lenses is to reduce the divergence of the beam of electrons. Because they reduce the divergence of the electron beam and allow convergence, a high intensified and the focused beam is obtained.

These lenses also aid in increasing the beam quality and also is extremely helpful in capturing electrons which possess low energy. It is very hard to capture electrons with low power, magnetic lenses does that with ease.

5. WORKPIECE AND WORK HOLDING DEVICE.

This is comprised of both metallic as well as non metallic material. The Workpiece is fixed and mounted on top of a CNC table. This table is very comfortable to move in all three directions and works efficiently to control the matching process and is very importantly helpful to keep it in shape. 

This set and arrangement is different and makes the whole process precise, efficient, and unique.

WORKING OF ELECTON BEAM MACHINING (EBM) – CARRIED OUT INSIDE THE VACCUM CHAMBER.

Electron Beam Machining working mechanism is as same as the laser beam machining process. Let’s collectively summaries the whole process into simple and easily understandable chunks. 

It’s precise and extremely fabulous machining performance will leave you surprised. Dive deep and understand the whole machining process mentioned below.

  • Firstly, Electron gun produces electrons with high velocity and intensity. This is basically a cathode and the electron particles moves towards the anode, whose placement is adjacent to the cathode tube. The temperature here nearly rises up to 2500°C due to the heat generated by the tungsten filament.
  • The electron beam now produced by the above-mentioned process passes through the magnetic lenses. These lenses strictly don’t allow the beam to diverge instead, help them to converge. This mechanism of convergence of electron beam provides a high quality to the beam of electrons.
  • After this process, the highly intensified and quality beam passes through electromagnetic lenses and deflecting coil. This process helps to focus the beam of electrons at a spot.
  • Now the high quality and intensified beam of electrons impinge on the workpiece. Here the energy interconversion takes place. The kinetic energy of beam of electrons is converted into thermal energy.
  • Because of the above-mentioned interconversions of energies, the material impinged is removed from the contact surface by vaporization due to high heat generation.

Electron beam machines exercises voltage in the range of 50 to 200KV to hasten the electrons to 50 to 80% of the speed of the electrons which is about 200,000 km/s.

NOTE:  All the above-mentioned processes must take place in a vacuum-sealed chamber. If not, the whole process is disturbed due to collisions of electrons.

MACHINING CARRIED OUT OUTSIDE THE VACCUM CHAMBER.

As it is fully not possible to maintain a vacuum sealed environment, this process came into action. Also keeping the cost and other parameters in mind, the machining process outside the vacuum chamber is a result of recent developments. 

It’s not like vacuum isn’t necessary, it is necessary but less when compared to the process done inside a vacuum chamber. Optimum vacuum is maintained within the electron gun and the gases are immediately removed after their entry into the system.

SOME APPLICATIONS OF ELECTRON BEAM MACHINING (EBM).

  • EBM is very effective in producing very small-sized holes( nearly about 100 micrometers to 2 millimeters).
  • EBM machining is used in aerospace industries for the turbine blade for nuclear reactors and some specific supersonic engines.
  • EBM is also used to produce holes in diesel injection nozzle.
  • EBM uses an electron beam that is much more powerful than a laser – so this heat source is used in metal 3D printing techniques.
  • EBM techniques are nowadays used in evidence-based medicine with many miraculous benefits.
  • Electron beam lithography is carried out using this machining process.

CHARACTERISTICS OF EBM MACHINING.

  • Mechanism through which material is removed : vaporisation and melting due to large amounts of released heat during machining process.
  • Maximum Material Removal Rate(MRR) : 10 mm3/ min.
  • Power consumption parameter : 450 W /mm3/ min.
  • Velocity of electron: 6 × 10^8m/s.

PARAMETERS OF EBM THAT HAVE A SIGNIFICANT INFLUENCE ON MATERIAL REMOVAL RATE.

Material Removal Rate is nothing but due to the high intensified beam of electrons impinged on the workpiece, energy interconversions take place and the material is removed from the contact surface either by melting or vaporization. Some main parameters are mentioned below:

  • Power control.
  • Spot diameter control.
  • Focal distance between the magnetic lenses.

ADVANTAGES OF USING ELECTRON BEAM MACHINING (EBM).

There are many marked advantages of using electron beam machining:

  • Micro-sized holes can be created using the EBM process.
  • EBM can machine any material irrespective of what is it made up of and it’s mechanical properties.
  • EBM machining produces an excellent surface finish. Further surface finishing is not required after this EBM machining. This property makes it unique.
  • Material with high reactivity can be machined easily and effectively, as the whole process is under a vacuum sealed environment.

DISADVANTAGES OF ELECTRON BEAM MACHINING (EBM).

Along with advantages, everything has its own disadvantages, so does EBM. The disadvantages of EBM are discussed below.

  • Capital cost is very high.
  • Operation skills required are very high.
  • The material removal rate is very low.
  • Regular Maintainance is mandatory.
  • A perfect vacuum-sealed environment is hard to attain. It’s almost impossible.

LET US DISCUSS SOME FREQUENTLY ASKED QUESTIONS ABOUT ELECTRON BEAM MACHINING IN A NUTSHELL:

1. Elaborate on the working principle of EBM.

When a high intensity of the beam of electrons impinges on the workpiece, energy interconversions take place I.e the kinetic energy of the electron is converted into heat energy. Basically, a thermionic reaction takes place. 

Due to the massive amounts of heat released the material gets vaporized from the workpiece. This principle is similar to the working of laser beam machining.

2. Why is there energy interconversion in EBM marching?

The basic concept about energy is that – Energy can neither be created nor be destroyed. It is just interconverted into different forms for the work to be done. In EBM, the kinetic energy (energy created by the motion of electrons) is converted into the thermal energy (heat). This heat is used to vaporize the material from the contact surface.

3. What is the reason behind using a total vacuum-sealed environment in EBM machining.

  • Vacuum sealing ensures a clean and contamination-free and a controlled environment.
  • The build material’s chemical specifications are dependant on the vacuum-sealed environment.
  • It helps the machining process to be precise and detailed.
  • The vacuum helps to prevent collision between electrons and the air molecules and helps the smooth functioning of the machining process.

4. What are the vacuum levels used in EBM?

There are basically three levels of vacuum used in the EBM machine. They are:

  • Full vacuum level : it is in the range of 10^-4 to 10^-5 mbar.
  • Partial vacuum level: it is in the range of 10^-2 to 10^-3 mbar.
  • Reduced pressure level : it is in the range of 10 to 10^-1 mbar.

CONCLUSION

Finally wrapping up the article in a nutshell with a conclusion.Among numerous and highlighted machining processes used these days, one stood out for being unique more than others in the “Electron Beam Machining”. It is commonly referred as “EBM”. This machining process tackles may facets with the precision of a high-energy laser. In order, to work properly the EBM machining process must be vacuum-sealed, in a contained environment.

What I find impressive about EBM is it’s stupendous power. It has a potential to vaporize it’s target area, at 50% to 80% of the speed of light. Although EBM seems to be best, there are many drawbacks as well like mentioned above. Gratefully, the machine in use is not being touched by the laser, which implies less damage and most importantly it’s long life time and less waste. 

It is considered as environmentally best alternative technique. The whole process is broken down into easy and understandable chunks for the convenience. Go through the apparatus and the procedure of the machining which is genuinely impressive. It is notably precise and accurate.

Hope this article is informative enough and convenient for all of you to read and understand. Dive deep into the article for a better understanding. Tried to keep the article simple, easier yet compiled. Please feel free to drop your queries regarding BM machining. And also please let us know any suggestions and advises you wish us to add in the article, this helps us to serve you better than ever.

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